Emergency telecommunications networks have been established to respond to emergency telephone calls from the public. These "911 networks" were established and added to the existing public switched telephone networks ("PTN"). In such a 911 network, a person places an emergency telephone call (a "911 call") that is routed in through the PTN to an appropriate public service answering point ("PSAP"). The PSAP receives the 911 call and contacts the appropriate emergency agency, such as the fire department or police department.
As shown in FIG. 1A, a 911 call is generally routed through the PTN as follows. First, the 911 call 114 is sent through the line connected to the calling phone to an originating central office ("C.O.") 112 that is connected thereto. Second, the call is routed on a trunk 107 from the originating C.O. to a tandem switch 110. Finally, the tandem switch routes the 911 call over a trunk 106 directly to the PSAP 102. In some applications, the 911 call is sent directly to the PSAP by the C.O.
The tandem switch 110, or tandem office, is a complex software-controlled trunk-to-trunk switching system that routes the 911 call to the appropriate PSAP facility 102. The tandem switch 110 compares the number of the originating phone call to a database to determine which PSAP has jurisdiction over the 911 caller's location. The caller's phone number is transferred from the tandem switch to the PSAP facility 102 to be displayed on a terminal at the PSAP facility.
Currently, most PSAPs have a dedicated trunk line from the originating central office to the PSAP, often via the tandem switch. At any point in this dedicated path, a failure could happen. A failure could be caused by a cable break or dig-up, equipment failure, tandem hardware or software failure, or catastrophic damage from storm activity, flood, earthquake, and the like. When the dedicated 911 network fails, the 911 caller 114 often receives a false busy signal or ring and never contacts the PSAP facility 102 in an emergency. A malfunction in the 911 network during an emergency can be devastating.
To overcome this problem, 911 network backup systems have been developed that detect when a 911 caller attempts to contact a PSAP but fails to do so because of a malfunction in the 911 network. In response to the 911 call, these network backup systems reroute the call through other trunks or lines in the PTN, avoiding the severed cables, faulty tandem switches or malfunctioning C.O.
One known network backup system uses a pair of transceivers, a trunk diverter circuit 116 positioned proximate to a central office and a responder circuit 122, having its own PTN number, positioned proximate to the PSAP facility 102 (and/or proximate to the tandem switch 110). When the trunk diverter circuit 116 detects that a 911 call cannot reach its appropriate PSAP facility, this transceiver reroutes the 911 call by dialing the number of the responder circuit 122 through a PTN or cellular network route, and reroutes the 911 call through the newly established route.
After dialing a 911 call, the 911 caller 114 normally waits six to ten seconds from the last digit depressed on the telephone before the PSAP receives the call and the 911 caller hears a ringing signal. When the dedicated 911 network is malfunctioning and the network backup system is initiated, the 911 caller experiences this normal ten-second delay, plus additional setup time as the trunk diverter circuit 116 attempts to dial the responder circuit 122. This setup time can add up to nine seconds for a PTN route and up to forty seconds for a cellular route, even when the PTN/cellular trunks are not busy. If the trunks are busy, the network backup system would attempt to reroute the call through other preprogrammed routes, adding additional time to the 911 call.
In an attempt to compensate for these delays, the known network backup system provides several voice messages to the 911 caller informing them of the progress of their call, and hopefully keeping them on the line. During an emergency, the 911 caller may not stay on the line, or, if they do not understand the voice messages (e.g., the 911 caller does not understand English), the caller may hang up and attempt to redial. Again, the 911 call will be subject to the above delays as the network backup system attempts to reroute the new 911 call.
While the network backup systems reroute 911 calls when the 911 network malfunctions, these backup systems are subject to delays. These delays are significant for panicked emergency callers. Even if these emergency backup systems improve the speed of their performance, they are nevertheless subject to the delays inherent in the PTN and cellular networks.
Overall, the inventors are unaware of a 911 or other telecommunications network backup system that provides rapid response despite the delays inherent in PTN and cellular networks.